Process and plant for the manufacture of pure cellulose from vegetable fibers



Sept. 19, 1933. Q BQUVIER r A 1,927,541

PROCESS AND PLANT FOR THE MANUFACTURE OF PURE CELLULOSE FROM VEGETABLEFIBERS Filed June '22, 1932 3 Sheets-Sheet 2 Anne/9 hrs.- Cesarflour/er; Geo/yes Fa'uc/re, Edmond SyZI/IZ QSQ Q BE E 5 Sheets-Sheet 3 gass M BOUVIER El AL Filed June 22, 1932 CELLULOSE FROM VEGETABLE FIBERSPROCESS AND PLANT FOR .THE MANUFACTURE OF PURE M QQ Sept. 19, 1933.

- Patented Sept. 19, 19 3.

. 1,921,541 raocns's AND PLANT Fon rnn MANUFAC- TABLE FIBERS TUBE 0FPURE CELLULOSE FROM VEGE- Cesar Bouvier, Paris, and Georges Fouch,

La Eleche, and. Edmond Serum, La Combole-Lude, France Application June22. 1932 Serial No. erases,

, and in France July 1, 1931 5 Claims. (cl. aa-m Numerous processes arein use for the manufacture of cellulose from vegetable fibers, basedupon the treatment of ligneous fibers by caustic soda, sulphates orbisulphites. However, such processes have but a limited yield, andailorda cellulose of an inferior quality, and they will not permit thetreatment of allvegetable substances by the same bath, being alsoexpensive as a general rule. Attempts have been made to employsulphurous anhydride gas for the disaggregation of ligneous fibers, butsuch processes cannot be practically employed on an industrial scale.They will not produce an entirely pure cellulose, and are not adaptedfor the full recovery oi the sulphurous anhydride gas, and are thusexpensive, being also attended with some danger when the apparatus isemptied, as the apparatus still contain a considerable amount of thisgas.

The process, the subject-matter or the present invention, relates to theuse of sulphurous an -J ous anhydride can be entirely recovered, thusobviating all danger due to the operations in the presence of a certainamount of this gas remain= ing in the apparatus.

The said process comprises the use, in the known manner, of twoautoclaves or digesters adapted for alternate operation, wherein oneantoclave contains ligneous material and water subjected to the actionof the sulphurous anhydride, with suitable heating, and the secondautoclave is being emptied, the same amount of sulphurous anhydridebeing successively employed in the two autoclaves. i v

The characteristic features of the invention consist in the fact that avacuum is produced in the autoclave filled with ligneous substances, be=fore the water is supplied to the same, and that the vacuum is alsoproduced upon the water during its delivery therein; the lower part ofthe said autoclave into which the sulphurous anhy= dride is suppliedfrom the other autoclave is subjected to an energetic cooling which ismaintained during the whole time of this introduction, whereby the saidsulphurous anhydride will 'be better dissolved, and the anhydride canalso be recovered in an approved manner and without recourse to anauxiliary autoclave.

The material is preferably cooled by a. circula tion of cooling brine ina worm-tube mounted in a chamber which is formed at the lower part ofeach autoclave and is separated from the main body of the same, whichchamber contains only the solution of the sulphurous anhydride.

In order to facilitate the extraction of the sulphurous anhydride fromthe autoclave engaged in the treatment, and to provide for its totalre.- covery, it is preferable to use a condenser upon the piping of theapparatus which withdraws the sulphurous anhydride gas from oneautoclave and delivers it into the other, and said condenser serves tocool the gas in'circulation, thus furthering'the suction of the gas.

The worm-tubes employed for the heating oi the material during thecookingv operation are preferably mounted in the said chambers situatedat the lower part or the autoclaves.

The said invention is disclosed in the follow ing descriptionillustrated icy the accompanying drawings.

Fig. 1 is a diagrammatic elevational view, with parts in section, of anapparatus embodying the said invention.

Fig. 2 is a diagrammatic view of a corresponding plant.

Fig. 3 is a plan view of a plant comprising several pairs of autoclaves.

In the form oi construction shown in Figures l and 2, the apparatusembodying the said proc= ess comprises two autcclaves l and 2 which areadapted for alternate action, each or which consists of a stationaryvertical cylinderv of large capacity preferably oi steel, and faced onthe innor wall with an adherent lining of lead, Such cylinders willwithstand a pressure of at least 15 lags. per em A pump compressorapparatus 3 operates with the autocla'ves for the suction and deliveryof the S02. The portion of the pump in contact with the gas should bemade. of a non-rusting metal; it should have a great cooling surface,and should operate with a vacuum oi at least G of mercury and acompression of at least dlrgs. per crn A condenser serves. to cool thegas withdrawn from the autoclaves. A set ofpiping 5-6, pro vided withsuitablecocks, serves for suction and delivery of the S0: for either ofthe autoclaves, and the cooling condenser may be used in the suctioncircuit; the two apparatus may also be connected together by the use oftwo pairs oi. pipes, and in each one pipe extends to the lower chamberof one of the digesters, whilst the other is connected at the top of theother digester.

The apparatus further comprises a. generator of units oi. cold by asuitable brine circulation (not shown), with the use of a pump. It alsoincludes a generator of heat by the use of steam (not shown) for thecooking, whose temperature may vary between and 110. C. according to thekind of wood to be treated and the rate at which the cooking is to beeffected. A dry vacuum pu'mpyknown per se, is also employed.

At the bottom of each digester is a relatively small chamber 7, of whichone side is formed by the lower wall of the digester and the upper sideby a false bottom 8a consisting of a metal which has been madenon-rusting, andit supports, at a very small distance, a second falsebottom of a perforated non-rusting metal which serves as a support forthe charge of fibersunder treatment.

In each autoclave, these two false bottoms are pierced at the centerwith an aperture upon which is mounted a vertical conduit 9 which risesto the level of the bath. On the top of said conduit is a cap whichallows the solution to pass through, but retains the fibers undertreatment, These conduits are pierced with orifices for the circulationof the liquid.

' In the lower chamber 7 of each autoclave is mounted a set ofworm-tubes 10 of non-rusting metal, adapted for a steam circulationaffording the heat necessary fgr the cooking as well as a set of wormtubes 11 of a like metal, adapted for the circulation of brine for theproduction of the cold required for the recovery of the S02. Thischamber 7 is used exclusively for the solution, and thus a rapid heatingor cooling effect can be obtained.

When the steam circulates in the worm-tubes, which are constructed inview of a surface of great eificacity, the liquid is rapidly heated, andthis affords a strong upward circulation in the vertical conduit 9, anda strong downward circulation around the said conduit, whereby the wholemass willbe rapidly heated.

On the contrary, when the cooling brine'iscirculated, only the chambercontaining the wormtubes need be cooled.

The upper part of each autoclave is closed by a bolted cover 12 which isof large size to permit the proper loading of the apparatus.

At the lower part of each autoclave is provided one or two largeapertures closed by bolted covers 13, for the discharge of the fibersafter the cooking. Along the cylindrical body of the apparatus aremounted level ganges, by which the operation can be suitably followed.The whole apparatus 'is covered with heat-insulating mate- Various necksare provided for connecting the autoclaves with the' several parts ofthe plant, such as a neck 14 for connecting with the vacuum pump, a neck15 for the SO: pump, a neck 16 for the water supply, a neck 17 foremptyin a neck 18 for the steam supply, and necks 19a, 19b for thecoldbrine supply.

The set of piping and cocks for the circulatio is clearly shown in thedrawings. L

The cycle of operations is as follows.

After the fibers have been loaded into one of the digesters and thedoors closed, the dry vacuum pump is operated in order to produce avacuum in this digester. When the proper vacuum has been reached, theoperator opens the connectionrbetween the autoclave and the watersupply, while continuing to produce the vacuum, which is maintained fora few minutes after the connection has been closed and the water hasreached its level. This vacuum serves in the first place to withdraw theair from the fibers and then the air dissolved in or brought over by thewater, thus preventing subsequent combinations from being made.Concurrently with the and around the cold brine worm-tube. The watercontained in this space becomes much colder than the water in the otherpart of the apparatus, due to the fact that as the coldest water has thegreatest density, and as the lower chamber is out 01f to a great degreeby the false bottoms supporting the charge, no movement of convectionwill take place, and hence the whole amount of cold produced by theworm-tube is confined to this lower chamber, hence the temperature atthis point will soon become low enough to provide for-a strong solution.All risk of freezing is obviated, due to the presence of S02.

When the proper amount of S02 has been introduced, the brine circulationis stopped, the worm -tube becomes emptied, and steam is supplied to theheating worm-tubes for the cooking, whose duration depends upon thenature of the fibers under treatment, the strength of the solution andthe temperature. It is possible to reach a pressure of 12 kgs. per cmand a temperature of C. in order to perform the cooking operation infour hours, without inconvenience as regards the purity of the celluloseor the strength of the apparatus which have been constructed for thepurpose.

When the cooking operationhas been completed, it is then resuired toproceed with the recovery ofthe S02, and the wholeof the SO:

used in the cooking operation which is now completed, is circulated intothe second autoclave, in which it acts to. decompose the material, thenreturning to the first, and so on for a great number of operations.

In the first place, this second autoclave is subject to the samepreliminary preparations as described for the first, that. is, loadingwith the fibers, vacuum, water supply brine circulation, vacuum.Thesediiferent preparatory operations are commenced at the proper timeduring the cooking inthe first autoclave, so that the recovery maycommence 'when the brine circulation has once exercised its coolingaction.

At this time, the operator opens the upper connection between the twoautoclaves; the connecting pipe leads from the top of the firstautoclave to the bottom of the second, and into the lower free spacefilled with liquid, surrounding the cold brine worm-tube. Due to thepressure prevailing in the first autoclave and to the cold and thevacuum in the second, the gas flows rapidly into this latter and is soondissolved.

' During this time the cold brine is constantly "incirculation, and itabsorbs the heat from the hot gas and from the heated solution. In a fewmoments the greater part of the SO: gas and a small amount of watervapour has circulated from the first to the second autoclave. Thepressures thus become balanced. Then follows the effective recovery ofthe $02 by means of the compressonused for this gas, whereby all the 80:re-

mining in the first autoclave is removed. For this purpose, the operatorclous the connection at the middle of the piping, and then sets thecompressor-pump in operation, and opens the valves for the suction anddelivery. The compressor, which is mounted ina branch circuit betweenthe two autoclaves, "withdraws through the aforesaid cooler from thefirst autoclave and delivers by pressure into the second autoclave andaround the brine worm-tube, and thus the pressure will fall in a veryshort time, and the vacuum is produced in the first autoclave, whilstunder the action of the cold the pressure has remained almost constantin the second autoclave.

Under the influence of the vacuum, meson cannot remain dissolved in thewater, and it circulates entirely from the-first autoclave to thesecond, and hence this second autoclave is entirely provided for anothercooking operation.

It is simply necessary to close off the upper connections to stop thepump-compressor apparatus and to circulate the steam, after stopping thebrine circulation, in order to commence another operation. J 3

During the coooking operation, the first autoclave is discharged and itscontents placed apart, and it is again filled and the same cycle ofoperations is continued.

' The crude cellulose thus obtained is first washed in hot water for thefinal removal of the organic substances surrounding the fibers. This hotwater can be economically obtained by circulating, through a heating andcooling apparatus, the hot water charged with dissolved organicsubstances pertaining to the autoclave in which the cooking has justbeen completed.

The cellulose is then subjected to the various manipulations dependingupon the use which is to be made of the same.

The saidprocess is adapted for the treatment of all varieties of wood orplants whether of a hard or resinous nature and of all ages, forinstance bamboo, dwarf-palm, ali'a or straw of all kinds, cut fine andmacerated in water, and in general, all ligneous or fibrous substances.

The said plant may comprise several pairs of autoclaves which areoperated as herein disclosed, as shown in Figure 3 of the drawings.

Obviously, the invention is not limited to the forms of constructionhereinbefore specified, and various other forms of apparatus may beemployed.

we claim:

l. A process for the manufacture of cellulose by the use of allvarieties of vegetable fibers, comrising the use of sulphurous anhydridein the lmown manner for the disaggregating of'such fibers in twoautoclaves adapted for alternate functioning, which process provides forthe manufacture of pure cellulose, with the total recovery of thesulphurous anhydride, characterized by the fact that a vacuum isproduced in the better dissolved and the anhydride can also be recoveredin an approved manner and without recourse to an, auxiliary autoclave.

2. An apparatus embodying the process claimed in claim 1, characterizedby the fact that each of the autoclaves comprises at the lower part 'achamberwhich is separated from the main chamber and in which isexclusively circulated the sulphurous anhydride solution, and furthercomprises a vertical conduit connecting the said chamber with the upperpart of the autoclave, said chamber containing a steam worm-tubeaffording the heat required for the cooking as well as a worm tubeadapted for a cold brine circulation adapted for cooling purposes.

3. A plant as claimed in claim 2, characterized ,by the fact that acooling condenser is mounted in the suction circuit between thepump-compresser set adapted for the recovery, and the autoclaves, whichcondenser is adapted to cool the gas and to facilitate the withdrawal ofthe sulphurous anhydride from the autoclave.

4. A plant as claimed in claim 2, characterized by the fact that itcomprises, two autoclaves provided at their lower parts with worm-tubechambers, a pump for sulphurous anhydride, a cooling condenser, a-set ofpiping, with cocks, which is adapted for suction and delivery for eitherof the autoclaves, by which the cooling condenser may be mounted in thesuction circuit and the two autoclaves may be connected to-.

